setting: Always remove Left-handed mode setting for non-phones

Right now, this option is only removed if you have a navigation bar
enabled and you aren't a phone.  This leads to UI wonkiness on
devices that allow the navigation bar to be toggled on/off:

* Enable the navigation bar.
* Navigate elsewhere and back to Buttons (force it to reload)
* Settings >> Buttons now contains a (grayed out) Left-handed mode.
* Enable the navigation bar.

Now Left-handed mode is available as an option even though it
shouldn't be.

Change-Id: Ifb3cdd18a014edffaf8bc53c46fc3c2f7a681370
settings: Avoid NPE in NfcTrigger when device doesn't support NFC

Change-Id: I7775540a752b6f31f8c5bb51eaf20e566b4858a5
Settings: Reduce volume to safe level when headset is connected (1/2)

This is a safety feature for users who opt to raise volume above the designated
safe level while using a headset.

Currently when a user does this they are provided with no protection against
dangerously high volume levels until the next time the headset volume warning
is displayed.

This patch adds an optional feature to ensure volume is no higher than the safe
level every time a headset is connected.

Change-Id: I8ec35284a91a26511b0bc83fcc1578f38b8b4f40